Scanners are used to control the direction of propagation of a light beam. Scanners are frequently found in devices such as laser printers and bar-code readers. The three general categories of previous scanner devices are mechanical, electro-optical, and ultrasonic devices. The most commonly used devices have been mechanical scanners, which are based upon a mirror or set of mirrors attached to the turning axis of an electromagnetic actuator such as a galvanometer or electric motor. Limitations of prior mechanical scanners include their relatively large size, high power consumption, and limited scanning frequencies. Prior galvanic scanners are typically 20.times.20.times.50 mm or larger, with a mass exceeding 50 grams (excluding control electronics), a typical power consumption of 1 Watt, and a scanning frequency below 8 kHz. Prior rotating polygon scanners (a type of mechanical scanner employing mirror-faced polygons attached to the rotating axis of an electric motor) are typically 100.times.100.times.90 mm or larger (excluding control electronics), with a typical power consumption of 5 Watts or more, and a scanning frequency below 10 kHz.
Prior electro-optical and ultrasonic devices are expensive, have limited deflection angles, and experience high attenuation of reflected light beams. Their scanning frequencies can be higher, however, in the MHz range.
Micro-electromechanical scanners based on electrostatic actuation of a moving mirror have been reported, but these devices have achieved only small deflection angles and low efficiencies as compared to electromagnetic devices of approximately the same resonance frequency and size. See K. Petersen, "Silicon Torsional Scanning Mirror," IBM J. Res. Develop., vol. 24, pp. 631-637 (1980); and K. Gustafsson et al., "A Silicon Light Modulator," J. Phys. E: Sci. Instrum., vol. 21, pp. 680-685 (1988). These references demonstrated that, while silicon is an excellent structural material for manufacturing a monolithic resonant scanning mirror with very good fatigue resistance (i.e., with a long working lifetime), electrostatic actuation was inefficient for millimeter-scale devices, producing mechanical deflection angles of only about 2.degree..
The present inventor has previously reported micro-mechanical scanners using electromagnetic actuation via a coil attached to a rotor, where the coil was electrically connected to an external power supply. The interaction between a constant external magnetic field and the electric current flowing in the coil generated a torque that deflected the rotor of millimeter-scale devices to mechanical deflection angles of 10.degree.. These prior devices experienced mechanical fatigue in the conductive tracks used to supply electric power to the moving coil after 100 hours of operation at 1 kHz and 10.degree. peak-to-peak mechanical deflection of the mirror. These fatigue problems limited the utility of these devices. L. Ferreira, "Microscanner de Silicio" (in Portuguese), doctorate thesis presented at Universidade Estadual de Campinas, Campinas, Sao Paulo, Brazil (1994); L. Ferreira et al., "Micromechanical Galvanometric Light Beam Scanner," Proc. 1996 Science and Technology Workshop, Center for Advanced Microstructures and Devices, Baton Rouge, La. (April 1996); laid-open Brazilian patent application number 9500860-8 (in Portuguese), filed Feb. 21, 1995.